Substantial effort and expense have been devoted to the development of electronic document processors which are capable of performing various document processing functions, including facsimile transmission and reception, computer printing, and document editing and storage. One of the basic goals has been to efficiently and economically combine such an electronic document processing capability with a more or less conventional photocopying capability. See, U.S. Pat. No. 4,241,990, which issued Dec. 30, 1980 on an application of T. Fisli entitled "Multi-Purpose Optical Data Processor", and U.S. Pat. No. 4,374,617, which issued Feb. 22, 1983 on another application of T. Fisli entitled "Multi-Function Document Processor".
As is known, an electro-optic element having a plurality of individually addressable electrodes may be employed as a multigate light valve for electro-optic line printing. See, U.S.Pat. No. 4,281,904, which issued Aug. 4, 1981 on an application of R. A. Sprague et al. entitled "TIR Electro-Optic Modulator with Individually Addressable Electrodes". Also see, "Light Gates Give Data Recorder Improved Hardcopy Resolution," Electronic Design, July 19, 1979, pp. 31-32; "Polarizing Filters Plot Analog Waveforms," Machine Design, Vol. 51, No. 17, July 26, 1979, p. 62; and "Data Recorder Eliminates Problem of Linearity," Design News, Feb. 4, 1980, pp. 56-57.
Indeed, significant progress has been made in developing such light valves and in applying them to electro-optic line printing. For example, a copending and commonly assigned U.S. patent application of R. A. Sprague, which was filed Sept. 17, 1980 under Ser. No. 187,911 on an "Electro-Optic Line Printer," shows that an image represented by a serial input data stream may be printed on a standard photosensitive recording medium through the use of a multigate light valve that is illuminated by a more or less conventional light source. That disclosure is of interest primarily because it teaches input data sample and hold techniques for minimizing the output power required of the light source. Furthermore, a copending and commonly assigned U.S. patent application of W. D. Turner, which was filed Sept. 17, 1980 under Ser. No. 187,936 on "Proximity Coupled Electro-Optic Devices," teaches that the electrodes and the electro-optic element of a multigate light valve may be physically distinct components which are pressed or otherwise firmly held together to achieve "proximity coupling." Moreover, U.S. Pat. No. 4,367,925, which issued Jan. 11, 1983 on an application of R. A. Sprague et al. entitled "Integrated Electronics for Proximity Coupled Electro-Optic Devices," shows that it is relatively easy to make the necessary electrical connections to the many electrodes of a typical proximity coupled multigate light valve if the electrodes are formed by suitably patterning a metallization layer of, say, a VLSI silicon electrode driver circuit. A further copending and commonly assigned U.S. patent application of W. D. Turner et al., which was filed Sept. 17, 1980 under Ser. No. 187,916 on "Differential Encoding for Fringe Field Responsive Electro-Optic Line Printers," teaches that the number of electrodes required of a multigate light valve for line printing at a given resolution is reduced by a factor of two if the input data is differentially encoded.